Eight patients with an inflammatory abdominal aortic aneurysm are described. They constituted 3.1% of all aortic aneurysms operated in the period 1981-1990. All presented with abdominal complaints and/or backache, and an elevated erythrocyte sedimentation rate (ESR); 3 had significant weight loss. The discovery of the aneurysm was considered a non-related finding except for 2 patients for whom the correct diagnosis was suggested by CT scan. Except for the aortic dilatation, the clinical and histopathological features of the inflammatory aneurysm resembled those of idiopathic retroperitoneal fibrosis with obstruction of the ureters and involvement of the duodenum by extensive perianeurysmal inflammation with infiltrates of mononuclear leukocytes and varying degrees of fibrosis. Although the triad of abdominal complaints and/or backache, an elevated ESR and weight loss has been proposed to suggest the diagnosis, the positive predictive value of these parameters was at best 22%. Additional studies, including CT scan, have to be performed to exclude, among other factors, vasculitis. Treatment should aim at repair of the aneurysm. Resolution of the inflammatory process after operation is frequently observed. Immunosuppressive therapy should only be used with caution, considering the possible increased risk of rupture.